Within Teamwork.com, you can lock a notebook while you are editing it so nobody else can edit the notebook at the same time.
To lock a notebook, go to the Notebooks tab of your project.
Hover over the notebook you want to edit, and you will see the Edit Notebook option.
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When the notebook is open, you will have an option to lock the notebook, in the top right corner.
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Once you have locked the notebook, the button will change to Unlock.
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While the notebook is locked, it a key will be shown in the notebook icon in the list of notebooks.
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Other users who open the notebook will see a message telling them it is locked for editing.
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Note: Site and project administrators can unlock notebooks locked by other users.
For more information, see: Creating a Notebook